Zero phase shift selective amplifier



Sept. 4, 1945. G. E. OBERWEISER ZERO PHAS-E SHIFT SELECTIVE AMPLIFIER I Filed Oct. 30, 1943 4 Sheets-Sheet l www: a; @su

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G. E. OBERWEISER ZERO PHASE SHIFT SELECTIVE AMPLIFIER linz-.rmiv

Filed Oct. 30, 1943 4 Sheets-Sheet 2 I INVEN TOR.

Sept 4, 1945 G. E. oBERwr-:ISER 2,383,984

ZERO PHASE SHIFT SELECTIVE AMPLIFIER Filed OCT.. 50, 1943 4 Sl'leeLs-Shec-zrl 5 Sept. 4, 1945. Q E, OB'ERWElsER 2,383,984

ZERO PHASE SHIFT SELECTIVE AMPLIFIER I Filed OCT.. 50, 1945 4 Sheets-Sheet 4 atented Sept. 4, 1945 LIFIER Gilbert E. Oberweiser, Cedar Rapids, Iowa, assignor to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Application October 30, 1943 Serial No. 508,334

v 12 claims.

My invention relates broadly to selective electrical amplifier systems and more particularly to a circuit arrangement for maintaining the phase shift of amplified energy throughout the transmission band at substantially zero.

One of the objects of my invention is to provide an improved circuit arrangement for a selective amplifier system in which means are included for maintaining the phase shift of the amplified signalling energy through the transmission band at substantially zero.

Another object of my invention is to provide a circuit arrangement for a selective amplifier system in a transmission channel in which phase shift of the transmitted energy in the transmission channel throughout any given frequency band is eliminated.

Still another object of my invention is'to provide a novel arrangement of coupled circuits for a transmission channel designed to prevent phase shift of the transmitted energy inthe transmission channel.

Other and further objects of my invention reside in the arrangement of parallel connected networks associated with the transmission vchannel of a transmission system for eliminating phase isolation tube through coupling resistors 6`| and condenser 8. 'I'he output circuit of isolation tube 5 connects through resistance network 9 to' the input circuit of the amplifier stage including tube I0. The output circuit of tube' I0- includes coupling-resistor II connected through condenser shift through the transmission system as set forth more fully in the specification hereinafter followed `by reference to the accompanying drawings, in

which: 4

Figure 1 diagrammatically illustrates a transmission channel including the novel arrangement of my invention for maintaining phase shift through the transmission channel at practically zero; Fig. 2 illustrates the phase characteristics of two of the parallel networks employed in association with the transmission channel in accordance with my invention; Fig. 3 illustrates the attenuation characteristic of one portion of the transmission channel; and Fig. 4 shows the chartransmission channel equipped with the protective circuits of my invention and illustrating the operation of the transmission channel withpractically no phase shift throughout the transmission band.

The amplifier consists of a, resistance'coupled main channel and two feedback circuits each consisting of two parallel-T networks connected in tandem as shown in Fig. 1. The amplifier in the main channel is provided with input terminals I connected to isolation tube 2 which connects to the amplifier stage including tube 3 through resistance coupled circuit il. The output circuit of amplifier stage 3 connects to the input circuit of acteristics of the selective amplifier system in the I2 with output terminals I4 of the selective am' pliiier. The main channel of the transmission system thus includes the combination o1' isolation tube 2 and amplifier tube 3 represented as a unit within dotted lines I5 and isolation tube 6 and amplifier tube I0 represented as a second unit within dotted line I6. 'I'he protective circuits for each of these units have been indicated generally within dotted lines I1 and I8 respectively. I have designated the main channel section I5 and the protective section Il as unit A while the main channel section I6 and its associated protective section I8 is designated unit B. I have designated section` I'I as feedback circuit A, all the elements of which are adjusted to the lower band limit of the frequency range of the associated main channel section I5. The section I8 has been designated as feedback circuit B,

the elements of whichare adjusted t0 the upper band limit of the frequency range of the main channel section I6. Each of the protectivecircuits includes a feedback loop that I have schematically represented at I9 and'ZIl to illustrate the action which takes place in both units A and B. The input path to the protective circuit extends from the output circuit of the main amplifier stage 3 to the two parallel-T networks represented at 2i and 22 connected in tandem. Network 2i includes capacity elements 23 and 2li and resistance element 25. Network 22 comprises resistance elements 26 and 2l and capacity element 28. These parallel-T connected networks connect to the input circuit of electron tube 29,' the output circuit of which is coupled to resistance coupled system to the input circuit of tube 3 I. The output circuit of tube 3l connects to the two parallel-T networks in tandem'illustrated at 32 and 33. Network 32 includes capacity elements 3i and 35 and resistance element 36. Network 33 includes resistance elements 3l and 38 and capacity element 33. The two parallel-T networks 32, 33 connect to the input circuit of .isolation dem.

The feedback circuit B constituting protective section I8 contains parts which are arranged in a symmetrical manner to the parts explained in connection with feedback circuit A and to designate th similarity and indentlty of the parts I have V.represented corresponding elements by the same reference characterswhich are primed in section I8 representing the correspondingly numbered parts in section l1. The elements of the feedback circuit B are adjusted to the upper band limit of the frequency range of the main channel section I6. The protective circuit of section I8 connects between the output circuit of tube l and the input circuit of tube I0 as shown in a manner similar to the arrangement in unit A.

Since the main channel has no tuned circuits, there will be practically no phase shift through this channel throughout any given frequency band. The 4phase characteristics of two parallel-T networks in tandem (each tuned to '455 kc.) are shown in Fig. 2. Thus, through any band width up to approximately 30 kc., the phase shift through the feedback circuit is practically constant at 180. The net phase shift through unit A (Fig. 1) is then zero for all relatively narrow frequency bands.

The attenuation characteristics of unit A are shown in Fig. 3. These are' approximately squared functions of frequency deviation, due to the use of the two parallel-T networks in tan- Staggering two such curves the proper amount and multiplying the ordinates result in nat top band pass curves shown in-Fig. 4. Unit B serves as the second zero phase shift unit with transmission characteristics properly staggered from those of unit A.

The net charasteristics of the whole amplifier, then, results in transmission characteristics as shown in Fig. 4, with practically no phase shift throughout this transmission band.

The band width of the amplifier is controlled by the two frequencies (F1 and Fa Fig. l) at which the two sets of T networks are nulled, and by the total gain around each feedback circuit which gives the proper slopes to each of the individual attenuation curves so that when the two are multiplied a flat-top curve will result. A narrow band-pass results in steeper attenuation curves, as shown in Fig. 4. This selectivity, or relative gain, is determined by the expression,

u is the amplifier gain taken around the total loop circuit. with no atenuation in either parallel-T network. a is the total attenuation input output #0 is a relative .plier gain can be controlled by using any portion of this gain in the main channel.

A proper number of tubesin the loop circuit is necessary to obtain proper degenerative phase relations 'between the feedback and input circuits and it will be understood that the circuits illustrated are merely for the purpose of explaining my invention and are not in any way indicative of the number of tubes employed.

The tandem pairsof parallel-T networks produce a 180 phase shift through themselves as shown in Fig. 2, since each individual parallel-T network has a phase shift of plus 90 on the high frequency side of null and minus 90 on the low side, these phase shifts being practically constant as the frequency approaches the null point. Two of these configurations in tandem, then. multiply the phase angle of each network by two which makes the resultant phase shift through the whole 180 on either side of the null frequency.

This apparent discontinuity at the null frequency will be of no consequence in steady-state applications, since in this case, a plus 180 phase shift and a minus 180 shift result in the same vector position. Furthermore, at the null frequency, the feedback vector is theoretically aero. Thus the phase shift of the amplifier at this point is not influenced by the feedback circuit.

It follows from the foregoing that the null frequency of each pair must be very nearly identical. If this condition is not satisfied the phase shift outside the two individual null frequencies will still be 180 but the phase shift between these two frequencies will be zero. This will destroy the zero phase shift characteristics of the amplifier, may cause oscillations, and will make the band pass characteristics of each unit (A and B, Fig; 1) have double peaks which would destroy the flat-top pass characteristics shown in Fig. 4. While I have described my invention in one of its preferred embodiments, I desire that it be understood that modifications may be made and no limitations upon my invention are intended other than may be imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. In a signal transmission system, a multistage electron tube amplifier comprising a multivple number of tubes each including input and ner tube to the transmission network, and feed back loop circuits connected between the output circuit of each amplifier tube and the input circuit of the said amplifier -tube for maintaining the phase shift of amplied energy throughout the transmission band at substantially zero.

2. In a signal transmission system. a multistage electron tube amplifier comprising a multiple number of tubes each including input and output circuits, an isolation tube having its input circuit connected with the transmission channel and its output circuit connected with one of said amplifier tubes, another isolation tube having input and output circuits, means for coupling the output circuit of said amplifier tube with the input circuit of said last mentioned isolation tube, connections between the output circuit of said last mentioned isolation tube and another of said amplifier tubes, circuit connections leading from fier tube to the transmission network, and feedback lo'op circuits comprising ycoupled electron tubes connected between-the output circuit of each amplifier tube and the' input circuits of the said amplifier tube for maintaining the phase shift of amplified energy throughout the transmission band at substantially` zero.

3. In a signal transmission system, a multistage electron tube amplifier comprising a multiple number of tubes each including inputand output circuits, an isolation tube having its input circuit connected with the transmission channel and its output circuit connected with one of said amplifier tubes, another isolation tube having input and output circuits, means for coupling the output circuitof said amplifier tube with the input circuit of said last mentioned isolation tube, connections between the output circuit of said last mentioned isolation tube and another of said` amplifier tubes, circuit connections leading from the output circuit of said last mentioned amplifier tube to the transmission network, and feedback loop circuits comprising coupled electron tubes and an isolation tube, connected between the output circuit -ofeach amplifier tube and the input circuit of the said amplifier tube for maintaining the phase shift of amplified energy throughout the transmission band at substantialLv zero.

4. In a signaly transmission system, a multistage electron tube amplifier comprising a multiple number of tubes each including input and output circuits, an isolation tube havingits input circuit connected with the transmission channel and its output circuit connected with one of said amplifier tubes, another isolation tube having input and output circuits, means for coupling the output circuit of said amplifier tube with the input circuit of said last mentioned isolation tube, connections between the output circuit of said last mentioned isolation tube and another of said amplifier tubes, circuit connections leading from the output circuit of said last mentioned amplifier -tube to the transmission network, and feedback loop circuits comprising coupled electron tubes with the output of the last of said coupled tubes connected to an isolation tube and connected between the output circuit -of each amplifier tube andthe input circuit of the said amplifier tube for maintaining the phase shift of amplified energy throughout the transmission band at substantially zero. y

5.In a signal transmission system, a multistage electron tube amplifier comprising a multipie number of tubes each including input and output circuits, an isolation tube having its input circuit connected with the transmission channel and its output circuit connected with one of said amplier tubes, another isolation Ytube having input and output circuits, means for coupling the output circuit of said amplier tube with the input circuit of said last mentioned isolation tube, connections between thev output circuit of said last mentioned isolation tube and another of said amplifier tubes, circuit connections leading from the output circuit of said last mentioned amplider tube to the transmission network, and feedback loop circuits comprising coupled electron tubes with a network connected in the input circuit thereto and an isolation tube connected in the output thereof and connected between the output circuit of each amplifier tube and the input circuit of the said amplifier tube for maintaining the' phase shift of amplified energy .throughout the transmission band at substantially zero. Y

6. In a signal transmission system, a multistage electron tube amplifier comprising a multiple number of tubes each including input and output circuits, an isolation tube having its input circuit connected with the transmission channel' and its outputl circuit connected with one of said amplifier tubes, another isolation tube having input and output circuits, means for coupling the output circuit of. said amplier tube with the input circuit of said last mentioned isolav tion tube, connections between the output circuit of said last mentioned isolation tube and another of said amplifier tubes, circuit connections leading from the output circuit ofl said last mentioned amplifier tube to the transmission network, and feed back loop circuits comprising coupled lelectron tubes with a pair of parallel-T networks one of said amplifier tubes, another isolation tube having input and output circuits, means for coupling the output circuit of said ampliner tube with the input circuit of said last mentioned isolation tube, connections between the output circuit of said last mentioned isolation tube and another of said amplifier tubes, circuit connections leading from the output circuit of said last mentioned amplifier tube to the transmission network, and feedback loop circuits connected between the output circuit of each amplifier tube and the input circuit of the said amplifier tube for maintaining the phase shift of amplified energy throughout the transmission band at substantially zero, one of said feedback loop circuits being tuned to the lower frequency band limit and the other of said loop circuits being tuned to the upper frequency band limit of the transmission system.

8. In a signal transmission system, a multistage electron tube amplifier comprising a multiple number of tubes each including input and output circuits, an isolation tube having its in.. put circuit connected with the transmission channel and its output circuit connected with one of said amplifier tubes, another isolation tube having input and output circuits, means for coupling the output circuit of said amplifier tube with the input circuit of said last mentioned isolation tube, connections between the output circuit of said last mentioned isolation tube and another of said amplifier tubes, circuit connections leading from the output circuit of said last mentioned ampli-l iier tube to the transmission network, and feedback loop circuits comprising coupled electron tubes connected between the output circuit of each amplifier tube and the input circuit of the said amplifier tube for maintaining the phase shift of amplified energy throughout the transmission band at substantially zero, and one of said feedback loop circuits being tuned to the lower frequency band limit and the other of said feedback loop circuits being tuned to the upper stage electron tube amplifier comprising a mu1 tiple number oi tubes leach including input, and output circuits, an isolation tube having its input circuit connected with the transmission channel and its output circuit connected with one of said amplifier tubes, another isolation tube having input and output circuits, means for coupling the output circuit of said amplifier tube with the input circuit of said last mentioned isolation tube, connections between the output circuit of said last mentioned isolation tube and another of said ampliiler tubes, circuit connections leading from the outputl circuit oi' said last mentioned ampliiier tube 'to the transmission network, and feedback loop circuits comprising coupled electron tubes and an isolation tube connected between the output circuit of each amplifier tube and the input circuit of the said ampliner tube for maintaining the phase shift of ampliiled energy throughout the transmission band at substantially zero, one of said feedback loop circuits being tuned to the lower frequency band limit and the other of said feedback loop circuits being tuned to the upper frequency band limit of the transmission system,

10. In a signal transmission system, a multistage electron tube amplifier comprising a multiple number of tubes each including input and output circuits, an isolation tube having its input circuit connected with the transmission channel and its output circuit connected with one of said ampliiier tubes, another isolation tube having input and output circuits, means for coupling the output circuit of said amplifier tube with the input circuit of said last mentioned isolation tube, connections between the output circuit of said last mentioned isolation tube and another of said amplifier tubes, circuit connections leading from the output circuit of said last mentioned amplifier tube to the transmission network, and feedback loop circuits comprising coupled eiectron tubes with the output of the last f said coupled tubes connected to an isolationY d5 tube and connected between the output circuit of each amplier tube and the input circuit of the said amplifier tube for maintaining the phase shift of amplified energy throughout the transmission band at substantially zero, one of said 50 feedback loop circuits being tuned to the lower frequency l'band limit and the other of saidloops circuits being tuned to the upper frequency band limit of the transmission system.

11. In a signal transmission system, a multi- 55 stage electron tube amplifier comprising a muloutput circuits, an isolation tube having its input circuit connected with the transmission channel and its output circuit connected with one of said amplifier tubes, another isolation tube having input'. and output circuits, means for coupling the output circuit of said amplifier tube with the input circuit of said last mentioned isolation tube, connections between the output circuit of said last mentioned isolation tube and vanother of said amplifier tubes, circuit connectionsleading from the output circuit of said last mentioned amplifier tube to the transmission network, and feedback loop circuits comprising coupled electron tubes with a network connected in the input circuit thereto and an isolation tube connected in the output thereof and connected between the output circuit of each amplifier tube and the input circuit of the said amplifier tube for maintaining the phase shift of amplied energy throughout the transmission band at substantially zero, one of said feedback loop circuits being tuned to the lower frequencyA band limit and the other'of said feedback loop circuits being tuned to the upper frequency band limit of the transmission system.

12. In a signal transmission'system, a multistage electron tube amplifier comprising a multiple number of tubes each including input and output circuits, an isolation tube having its input circuit connected with the transmission channel and its output circuit connected with one of said amplifier tubes, another isolation tube having input and output circuits, means for coupling the output circuit of said amplifier tube with the input circuit of said last mentioned isolation tube, connections between the output circuit of said last mentioned isolation tube and another of said amplifier tubes, circuit connections leading from the output circuit of said last mentioned amplier tube to the transmission network, feedback loop circuits comprising coupled electron tubes with a pair of parallel-T networks connected in the input circuit thereof and an isolation tube connected between the output circuit of each amplifier tube and the input circuit of the said amplifier tube for maintaining `the phase shift of amplied energy throughout the transmission band at substantially zero, one of said feedback loop circuits being tuned to the lower frequency band limit and the other of said loop circuits being tuned to the upper frequency band limit of the transmission system.

GILBERT E. OBERWEISER. 

